A liquid crystal display panel has two substrates between which liquid crystal is sealingly stored, and electrodes are formed on main surfaces of the substrates opposed together.
FIG. 27 is a schematic cross section of a liquid crystal display panel. Electrodes 24 are formed on a substrate 20 on a display side, and electrodes 25 are formed on an opposite substrate 21. Substrates 20 and 21 are adhered together by a seal member 22 with electrodes 24 and 25 opposed to each other. Spacers (not shown) keep a constant distance between substrates 20 and 21. A region surrounded by two substrates 20 and 21 and seal member 22 is sealingly filled with liquid crystal 23. In the present invention, a structure that includes liquid crystal sealingly stored between the two substrates, and is used as one liquid crystal display panel is referred to as an “individual liquid crystal display unit”.
As one of alignment modes of liquid crystal, there is a vertical alignment mode (VA type) in which liquid crystal molecules are aligned vertically with respect to the main surface of the substrate. In the state where no voltage is applied across the electrodes, the longitudinal directions of the liquid crystal molecules are aligned vertically with respect to the main surface of the substrate. When a voltage is applied across the electrodes, the longitudinal direction of the liquid crystal molecules changes from a direction perpendicular to the main surface of the substrate to a direction parallel to the main surface of the substrate. This operation changes a retardation of the liquid crystal layer so that the liquid crystal display unit can perform multi-level or gradation display.
In the liquid crystal display panel using the vertical alignment mode, retardation of the liquid crystal is not present when a voltage is not applied (i.e., “residual retardation” is not present). Therefore, the liquid crystal display panel of the transparent type generally employs a normal black mode in which a linearly polarizing plate 49 is adhered in a state of cross nicols to the main surface of each of substrates 20 and 21 on the display side and the opposite side shown in FIG. 27. By arranging the polarizing plates as described above, black display can be performed to an extent similar to that by the cross nicols of the polarizing plates, and good contrast can be achieved.
As the vertical alignment mode, such a circular polarization mode is known that uses a circularly polarizing plate formed of a combination of a polarizing plate and a λ/4 phase difference plate instead of the foregoing polarizing plate. Since the circular polarization mode can perform reflection display, the circular polarization mode is suitable for a reflection type or a semitransparent type of liquid crystal display device.
FIG. 28 is a cross section of a circularly polarizing plate based on a prior art (see, e.g., Japanese Patent Laying-Open No. 2003-121642). A circularly polarizing plate has a structure in which a linearly polarizing plate 32 is overlaid on a λ/4 phase difference plate 30. Linearly polarizing plate 32 is provided at its main surface with a transparent protection plate 33. The liquid crystal display panel can perform the display by the operations of the circularly polarizing plate and the liquid crystal. In the vertical alignment type of liquid crystal display panel, the liquid crystal layer causes a retardation difference depending on an angle of viewing the liquid crystal display panel, the view angle that allows appropriate display becomes narrow.
For example, when black display is being performed by the liquid crystal molecules of which longitudinal direction is perpendicular to the main surface of the substrate, it is preferable that the black is displayed in deep black at any view angle. However, this state weakens a black-white contrast ratio when viewing the liquid crystal display panel at an oblique view angle. Further, the color liquid crystal display panel causes so-called “color changes”, i.e., unintended changes in displayed color, and the monochrome liquid crystal display panel causes so-called “coloring”, i.e., addition of violet to monochrome display. For optically compensating for retardation, the vertical alignment type of liquid crystal display panel is provided at a main surface of λ/4 phase difference plate 30 remote from linearly polarizing plate 32 with a C-plate 31 serving as an optical compensation film for increasing the view angle.
FIG. 29 illustrates optical characteristics of the C-plate. Assuming that the C-plate has refractivities nx and ny in the directions parallel to the main surface of the C-plate as well as a refractivity nz in the direction of thickness, the C-plate exhibits characteristics of (nx=ny>nz). The C-plate is a birefringent layer of which optical indicatrix is negative uniaxial. The values of nx and nz of the C-plate are determined according to the form or configuration of the liquid crystal molecules used therein. By overlaying the C-plate on the circularly polarizing plate, the view angle can be increased.
FIG. 30 optically illustrates a usual λ/4 phase difference plate. nx and ny represent the refractivities in the directions parallel to the main surface of the λ/4 phase difference plate, and nz represents the refractivity in the direction of thickness of the λ/4 phase difference plate. Assuming that λ/4 phase difference plate has a thickness of d, the λ/4 phase difference plate satisfies the relationship of the following equation:(nx−ny)·d=(1/4)λ  (1)
The liquid crystal display panel satisfies the relationship of (nx>ny=nz). Thus, a general λ/4 phase difference plate exhibits positive refractivity characteristics. In the λ/4 phase difference plate of the circularly polarizing plate of the liquid crystal display panel, it is preferable to use nz of a smaller value (see, e.g., Japanese Patent Laying-Open No. H11-212077).
Japanese Patent Laying-Open No. 2003-90915 has disclosed an optical compensation film having a large Nz coefficient in the λ/4 phase difference plate. It is disclosed that the Nz coefficient of the λ/4 phase difference plate is preferably in a range of more than 1.1 and not more than 3 for achieving good view angle characteristics.
In the manufacturing process of the liquid crystal display panel, liquid crystal 23 must be sealingly stored between two substrates 20 and 21 as shown in FIG. 27. For storing liquid crystal 23, a dip method or a dispenser method may be performed. In these storing or applying methods, an annular seal member having an opening is arranged on one of the substrates, and the two substrates are adhered in advance together. Then, the liquid crystal is applied through the opening, and the opening is closed. In the dip method and dispenser method, the application of the liquid crystal and the closing are performed after adhering the substrates together.
In recent years, one-drop applying method (which will also be referred to as a “drop adhering method” hereinafter”) has been developed as a method of sealingly storing the liquid crystal between the two substrates. In the one-drop applying method, an annular seal member of a closed form is arranged on a main surface of one of the substrates. After applying a drop of liquid crystal to an area inside the annular seal member thus arranged, the two substrates are overlaid in a depressurized atmosphere. After adhering the two substrates, the pressure is returned to an atmospheric pressure to store the liquid crystal. In this one drop filling method, adhesion of the two substrates can be performed simultaneously with storing of the liquid crystal so that the manufacturing time can be remarkably reduced. Further, such an advantage can be achieved that a plurality of liquid crystal display units can be simultaneously formed in a grid like fashion between large substrates.
FIGS. 31 to 35 illustrate a manufacturing method of a prior art in which a circularly polarizing plate is adhered to an individual liquid crystal display panel (see Japanese Patent Laying-Open Nos. 2003-227925, 2003-232922 and 2003-57635). As shown in FIG. 31, the method prepares a λ/4 phase difference plate 35 taking a rolled form and having a lagging axis parallel to the longitudinal direction as indicated by an arrow 54, and a linearly polarizing plate 36 taking a rolled form and having an absorption axis inclined by 45° from the longitudinal direction as indicated by an arrow 55. λ/4 phase difference plate 35 and linearly polarizing plate 36 are arranged such that the longitudinal directions thereof are parallel to each other.
Then, as shown in FIG. 32, λ/4 phase difference plate 35 and linearly polarizing plate 36 are adhered together with their longitudinal direction parallel to each other. An optical film, i.e., a circularly polarizing plate 39 is formed by the adhesion, and is wound into a roll form again.
As shown in FIG. 33, a rectangle defined by a cutting frame 41 is cut off from circularly polarizing plate 39. One side of the rectangle thus cut is parallel to the longitudinal direction of circularly polarizing plate 39. This cutting step is generally performed such that circularly polarizing plates of a plurality of liquid crystal display units can be cut off later.
As shown in FIG. 34, portions each required for an individual liquid crystal display unit are cut off along cutting frames 42 from the circularly polarizing plate previously cut off.
As shown in FIG. 35, circularly polarizing plate 39 is finally adhered to a main surface of an individual liquid crystal display unit 10. In this case, the main surface of individual liquid crystal display unit 10 is adhered to the main surface of circularly polarizing plate 39 provided by the λ/4 phase difference plate as indicated by an arrow 61.
Patent Document 1: Japanese Patent Laying-Open No. 2003-121642
Patent Document 2: Japanese Patent Laying-Open No. H11-212077
Patent Document 3: Japanese Patent Laying-Open No. 2003-90915
Patent Document 4: Japanese Patent Laying-Open No. 2003-227925
Patent Document 5: Japanese Patent Laying-Open No. 2003-232922
Patent Document 6: Japanese Patent Laying-Open No. 2003-57635